This invention relates generally to hermetically sealed electronic devices and, more particularly, to an apparatus for drying the inside of such devices.
Electronic assemblies for use in a variety of harsh environments, such as in space, marine applications, or the human body, are sealed from the outside conditions by use of gas-tight (hermetically sealed) containers. Such containers, while sealing out external dust, air or moisture, also trap in whatever is inside the devices. Water vapor is one of the things that are trapped inside such devices. Since any water vapor that is present inside of an electronic enclosure is a potential contributor to corrosion and circuit shorting, it is desirable to somehow remove the water vapor from the air inside the device after it is sealed.
The moisture in the air inside of a sealed electronic device can be removed from the air by including a desiccant inside of the device. A desiccant is usually placed inside electronic devices immediately prior to closure of the devices. The desiccant removes the moisture from the air inside the device by trapping or absorbing it. A dry desiccant in some form is placed inside an electronic device as one of the last steps prior to closure of the device. The step of adding the desiccant to the device is usually done in a xe2x80x9cdry box,xe2x80x9d or xe2x80x9cweld glove box,xe2x80x9d and, that way, the desiccant is kept basically dry prior to placement in the device. If a desiccant was added to a device earlier and/or allowed to be exposed to the air for some time while the electronic device was being assembled, the desiccant would absorb an appreciable amount of moisture from the air and would thereby be ineffective in absorbing moisture from the air inside of the electronic device once it is sealed shut.
The fact that the desiccant must be added as one of the last steps in assembly of an electronic device places limits on the design and form of the desiccant and also on the design of the electronic device itself. Currently, the design of both must allow the desiccant to be easily added to a near completely assembled electronic device. In addition, the need for use of a xe2x80x9cdry boxxe2x80x9d or xe2x80x9cweld glove boxxe2x80x9d in the assembly of electronic devices obviously places limits on where the assembly of the device may take place.
A need, therefore, exists for an apparatus that allows a desiccant to be incorporated into an electronic device well prior to closure of the device without the desiccant adsorbing an appreciable amount of moisture from the air. A need also exists for a way to control when the desiccant will begin to absorb moisture. The present invention meets these needs, and more. The present invention includes a coating over a desiccant that is an effective barrier to moisture for a definable period of time. The present invention also provides a way to activate the desiccant at a specific time to begin absorbing moisture. The present inventive apparatus may be made in different shapes, sizes and forms that allow for different designs of the electronic devices themselves. The present invention also meets other needs that will become apparent from a review of the description of the present invention.
There is prior art that discloses coating desiccants with a surface treatment to limit adsorption by the desiccant. However, the prior art does not include any kind of activation strip or mechanism to begin the absorption at a certain time.
In its simplest embodiment, the present invention is an apparatus for drying the air inside of a hermetically sealed electronic device that comprises a desiccant part, an activation piece that is attached to said desiccant part, and a coating of a material with a low moisture vapor transmission rate that coats said activation piece and said desiccant part except where said activation piece and said desiccant part are attached.
The advantages of the present invention will become readily apparent to those skilled in the art from a review of the following detailed description of the preferred embodiment especially when considered in conjunction with the claims and accompanying drawings in which like numerals in the several views refer to corresponding parts.